Inner focusing lenses of high zoom ratio usually have an increased variation rate of a displacement of a focusing lens upon close-up photoshooting at a minimum objective distance from the leading end of the lens to the subject, and an attempt to raise a close-up performance at the minimum objective distance by means of a single focusing cam member causes focus to change greatly in the remaining zooming ranges, resulting in varifocal. Focusing cam curves, which perform a varifocal-zooming conversion, must be deliberately designed for appropriate zooming and focusing parameters. However, this leads to difficulties in ensuring a well-balanced cam configuration for the smooth zooming and focusing, and a curvature of focusing cams must be changed, or some other compensation must be made with the focusing cams.
In the prior art high zoom ratio lenses, the focusing lens is simultaneously rotated and displaced forward and backward during either the zooming or the focusing. Typically, guide grooves are defined in the focusing cam barrel to serve as cams along with pins fitted in the guide grooves to slide and trace in the guide grooves of the focusing cam barrel, which permits rotary components to turn for the focusing. During the zooming, the rotary components turn along the focusing cam barrel in bi-directions that determine an operable range of the focusing cams to adjustably obtain an appropriate displacement of the focusing lens (see Patent Document 1 listed below).
However, it is still harder to determine the operable range of the focusing cams so as to ensure the appropriate displacement of the focusing lens as well as the further enhanced close-up performance at the minimum objective distance without focal change in the entire zooming range. The zoom lenses of zooming ratio as high as 5×±α are typically of 5-layer configuration where a first cam barrel is inside a fixed barrel while a second cam barrel, a linear shuttle cam barrel, and a third cam barrel are disposed outside the fixed barrel one over another, and with such a configuration, the zoom lenses cannot reduce a diameter any longer. Such zoom lenses do not allow for anti-shake or image stabilization mechanism incorporated therein.
Some of the prior art high zoom ratio lenses have focus compensating cams and focusing cams disposed in the same rotary component to attain the desired displacement of the focusing lens (see Patent Document 2 listed below). However, such zoom lenses are typically configured so that the focusing lens is linearly moved during the zooming, and therefore, the zooming operation is simply adjusted by a fixed amount of compensation in any segment of the zooming range, which results in the compensation is insufficient to reduce the objective distance for the close-up photoshooting. In addition, this type of the high zoom ratio lenses encounter a problem that an outer diameters cannot reduce any longer because of their 5-layer configuration having first and second cam barrels, a linear shuttle barrel, and a third cam barrel outside a fixed barrel. This type of the zoom lenses do not allow for anti-shake or image stabilization mechanism incorporated therein.
Some other prior art high zoom ratio lenses include, as shown in FIGS. 10 and 11, a zoom linkage ring 14 inside a fixed barrel 12, a first cam barrel 16 inside the zoom linkage ring 14, a linear shuttle barrel 18 inside the first cam barrel 16, and a focusing cam barrel 20 inside the linear shuttle barrel 18. The first cam barrel 16 is engaged with the zoom linkage ring 14 with zoom linkage studs 40 intervening therebetween so that rotation of the zoom ring 30 can be transmitted to the first cam barrel 16. The first cam barrel 16 has 1st-cam-barrel guide cams with guide studs 39 used to move the first cam barrel along the optical axis, 3rd-lens-group guide cams with 3rd-lens-group guide studs 43 operatively fitted therein, and 4th-lens-group guide cams with 4th-lens-group guide studs 45 operatively fitted therein. The first cam barrel 16 also has 2nd-cam-barrel linkage studs 50 protruding outward at the leading end of the fixed barrel 12 opposite to a lens mount 10. The 2nd-cam-barrel linkage studs 50 are operatively fitted in longitudinal guide grooves defined in the second cam barrel 22 (see Patent Document 3 listed below).
In the above-mentioned high zoom ratio zoom lenses, the zoom linkage ring 14 is attached inside of the fixed barrel 12, the first cam barrel 16 is disposed inside the zoom linkage ring 14, and the linear shuttle barrel 18 is disposed inside the first cam barrel 16. The zoom linkage studs 40 couple the first cam barrel 16 with the zoom linkage ring 14 so as to transmit the rotation of the zoom 30 to the first cam barrel 16. In order to make the first cam barrel 16 move along the optical axis, the first cam barrel 16 has to be provided with the 1st-cam-barrel guide cams engaged with the 1st-cam-barrel guide studs 30, the 3rd-lens-group guide cams engaged with the 3rd-lens-group guide studs 43, and the 4th-lens-guide cams engaged with the 4th-lens-group guide studs 45.
However, the first cam barrel 16 is restricted in its entire extension along the optical axis, and this results in the 1st-cam-barrel guide cams, the 3rd-lens-group guide cams, and the 4th-lens-group guide cams being restricted in their respective entire extensions along the optical axis. Especially, in order to raise a zoom ratio, the third and fourth groups of lenses among others succeeding to the first and the second must respectively be given a greater stroke along the optical axis, but it is hard to accomplish a well-balanced adjustment among the guide cams within the restricted dimension of the first cam barrel 16 extending along the optical axis. In other words, there is no compromised solution in forced arrangement of the guide cams, and if there were, the guide cams are restricted more in their relative configurations and positions without freedom and idleness of design.
Moreover, as for an available entire extension of the fixed barrel 12, a stroke of the linear shuttle barrel 18 is increased as a displacement of the third group of lenses is increased, and this leads to another problem of losing a steady fitting-hold or anchor-hold of the linear shuttle barrel 18 on the fixed barrel 12 during displacing the linear shuttle barrel for the telephoto-shooting to eventually lose the required stability of the lens barrel. Additionally, this type of the zoom lenses do not allow for anti-shake or image stabilization mechanism incorporated therein.
On the other hand, at an attempt to configure a lens barrel so that its radial dimensions can be reduced, there has been developed a lens barrel having a shake-compensating unit and a lens frame holding lens pieces both of which are included as at least part of a photoshooting optics, and such a improved lens barrel has a restrictor located in the shake compensating unit so as to restrict rotation of the lens frame (see Patent Document 4).
Patent Document 1:                Japanese Patent Preliminary Publication No. H8-304684        
Patent Document 2:                Japanese Patent Preliminary Publication No. 2000-89086        
Patent Document 3:                Japanese Patent No. 3689379        
Patent Document 4:                Japanese Patent Preliminary Publication No. 2007-79241        
The present invention is made to overcome the aforementioned disadvantages in the prior art zoom lens barrel, especially, the prior art inner focusing zoom lens barrel, and accordingly, it is an object of the present invention to provide an improved inner focusing zoom lens barrel that implements a zoom ratio as high as 15×±α and that ensures a well-balanced cam configuration for the smooth zooming and focusing and facilitates to incorporate anti-shake mechanism.
It is another object of the present invention to provide an inner focusing zoom lens barrel that is capable of attaining a sufficient close-up performance at the minimum objective distance from the leading end of the zoom lens barrel to the subject and of minimizing change in focus throughout the entire zooming range and that is reduced in its outer diameter.
It is further another object of the present invention to provide an inner focusing zoom lens barrel that is imposed reduced restrictions on configurations and positions of guide cams and that keeps a steady fitting-hold or anchor-hold of a linear shuttle barrel on a fixed barrel during displacing the linear shuttle barrel for the telephoto-shooting to eventually retain the required stability of the lens barrel.